The very last portion of a book proposal is your biography. This is the chance to brag a little bit about yourself and to tell the editor/agent pertinent information about yourself. For example, say you've written a middle grade novel where the kids are running around trying to outwit an ancient Mayan prophecy and you also happen to be the world's current leading expert on all things Mayan, that would be something to include in your biography. Or perhaps, you run a blog with 1500 followers that offers advice to parents adopting children from China, and you wrote a picture book about a little boy going with his parents to pick up his new baby sister from China. Again, that would be something to mention.
Also, this is the time to remind the agent/editor (you've already mentioned it in the cover letter) if you are a published author. You can also enclose a one page list after your bio of your top publishing credits. However, again, use your discretion. If you've published 45 magazine articles, 12 short stories, 16 novels and edit an online journal, you don't want to list every single credit. Hit the highlights.
To practice your bios, go to the Forum and post it. No one will criticize what you've done, we'll just give you feedback so you can show yourself in the best light.
And that my friends, concludes Book Proposal March. You have now read (and in some cases practiced) all of the elements of a good book proposal. But don't stop practicing. Remember, in a couple of weeks I will be holding a Book Proposal contest. The top 5 book proposals will receive a free critique of their proposal (including the sample chapters/manuscript in the proposal), and ALL entries in the contest will be considered for publication by CBAY Books. You can submit any genre, any age, anything -- even stuff you might not think is appropriate for the CBAY lists. After all, you could still win a critique, and I'm also considering an ebook original imprint that will publish more than SF/fantasy. I'm thinking of broadening my scope, so to speak, but I have to see what's out there before I decide.
Rules, information, and deadlines for the contest will go up tomorrow. So, keep posting on the Forum (in any of the parts of a book proposal, not just author bios) to get your book proposal in the best shape possible.